Inductive conductivity sensors for ascertaining electrical conductivity of a medium include, essentially, two toroidal coils, surrounded by the medium. The coils bound a passageway for the medium and are usually arranged coaxially, with a first of the coils, as exciter coil, inducing an electrical current in the medium. Such electrical current is then registered by the second coil. The principle, per se, is established in industrial process measurements technology and documented in a large number of examples of the patent literature, for example in U.S. Pat. No. 3,603,873 and German Offenlegungsschrift DE 198 51 146 A1.